/* --------------------------------------------------------------------------
CppAD: C++ Algorithmic Differentiation: Copyright (C) 2003-17 Bradley M. Bell

CppAD is distributed under multiple licenses. This distribution is under
the terms of the
                    Eclipse Public License Version 1.0.

A copy of this license is included in the COPYING file of this distribution.
Please visit http://www.coin-or.org/CppAD/ for information on other licenses.
-------------------------------------------------------------------------- */

/*

$begin ipopt_solve_retape.cpp$$
$spell
	Retaping
	retape
	cppad_nlp
	IpoptDir
	CppAD
$$

$section Nonlinear Programming Retaping: Example and Test$$
$mindex retape ipopt_solve$$

$head Purpose$$
This example program demonstrates a case were the $code ipopt::solve$$
argument $cref/retape/ipopt_solve/options/Retape/$$ should be true.

$code
$srcfile%example/ipopt_solve/retape.cpp%0%// BEGIN C++%// END C++%1%$$
$$

$end
*/
// BEGIN C++
# include <cppad/ipopt/solve.hpp>

namespace {
	using CppAD::AD;

	class FG_eval {
	public:
		typedef CPPAD_TESTVECTOR( AD<double> ) ADvector;
		void operator()(ADvector& fg, const ADvector& x)
		{	assert( fg.size() == 1 );
			assert( x.size()  == 1 );

			// compute the Huber function using a conditional
			// statement that depends on the value of x.
			double eps = 0.1;
			if( fabs(x[0]) <= eps )
				fg[0] = x[0] * x[0] / (2.0 * eps);
			else
				fg[0] = fabs(x[0]) - eps / 2.0;

			return;
		}
	};
}

bool retape(void)
{	bool ok = true;
	typedef CPPAD_TESTVECTOR( double ) Dvector;

	// number of independent variables (domain dimension for f and g)
	size_t nx = 1;
	// number of constraints (range dimension for g)
	size_t ng = 0;
	// initial value, lower and upper limits, for the independent variables
	Dvector xi(nx), xl(nx), xu(nx);
	xi[0] = 2.0;
	xl[0] = -1e+19;
	xu[0] = +1e+19;
	// lower and upper limits for g
	Dvector gl(ng), gu(ng);

	// object that computes objective and constraints
	FG_eval fg_eval;

	// options
	std::string options;
	// retape operation sequence for each new x
	options += "Retape  true\n";
	// turn off any printing
	options += "Integer print_level   0\n";
	options += "String  sb          yes\n";
	// maximum number of iterations
	options += "Integer max_iter      10\n";
	// approximate accuracy in first order necessary conditions;
	// see Mathematical Programming, Volume 106, Number 1,
	// Pages 25-57, Equation (6)
	options += "Numeric tol           1e-9\n";
	// derivative testing
	options += "String  derivative_test            second-order\n";
	// maximum amount of random pertubation; e.g.,
	// when evaluation finite diff
	options += "Numeric point_perturbation_radius  0.\n";

	// place to return solution
	CppAD::ipopt::solve_result<Dvector> solution;

	// solve the problem
	CppAD::ipopt::solve<Dvector, FG_eval>(
		options, xi, xl, xu, gl, gu, fg_eval, solution
	);
	//
	// Check some of the solution values
	//
	ok &= solution.status == CppAD::ipopt::solve_result<Dvector>::success;
	double rel_tol    = 1e-6;  // relative tolerance
	double abs_tol    = 1e-6;  // absolute tolerance
	ok &= CppAD::NearEqual( solution.x[0], 0.0,  rel_tol, abs_tol);

	return ok;
}
// END C++
